I'm on a slower internet connection and I see it on every single new site I visit - regardless of what it is powered by. The only thing that makes sense is after upgrading to a new version, your browser sees there are all "new" files and goes and fetches it again.

I didn't see the white flash on subsequent reloads of any of the sites mentioned above that I spot-checked.

The wp-head call is a hook many plugins use to load extra scripts needed. remove it from the theme (which isn't a core hack, really) would stop any plguin from using that call correctly. And stop any extra code loading.

Hi Andrea,
I was just eliminating that from the possible reasons, as far as I can make out it is when the two lines above are in the <head></head> section that the flash happens, I am testing on local host and adding things one at a time.

As soon as a plugin add the second line in the section I get the flash.

The Devs are aware of the situation

Hi Ipstenu,
I checked the WordPress trac today I could not see a ticket for this problem?

.... and I just tried the jQuery fix suggested by Nisien. Seems to help a little, in that I sometimes don't get a flash, but I usually do. I also realise other plugins might cause a problem, it's just less consistent.